Tappet plate pressing on Sector Gear

[RainyEyes]

Trying to reshim my g36 perfectly, and I'm running into a problem where the sector gear ALWAYS causes some sort of motor whine.

I've concluded that my bevel-pinion gear shimming is at least near perfect because I've decided to do the slow and painful way of shimming by slowly increasing/decreasing increments of shims from one side to the other with ONLY the bevel gear installed and running the motor to listen for whine until there is minimal/none.

When I add the spur gear - no motor whine.

When I add in the sector gear - it starts to whine periodically. I hear a high pitch noise coming and going, so I have no idea what's going on, since it should be consistent right? This is without a tappet plate and cut-off lever installed by the way.

Could it be because the bushings are press fitted? I tried removing it but I've only been able to remove 4/6 with fear of needing to use the force of Thor's hammer to remove the remainder. I'm uncertain if the bushings are seated at an angle, and the sector gear bushing is 1 of the 2 that I can't remove... The other bushings I've had to remove since they weren't sitting flush in the gearbox and needed a bit of filing.

So I thought hey, whatever, no biggie. I install the tappet plate and it's sitting on the sector gear at an elevated angle. I don't think this is normal? I've shimmed the sector gear so high to accommodate the bevel that it's actually forcing the tappet plate to push down on it so that I only need to shim the bottom and not the top of the sector gear...

What should I do?

[pestobanana]

1. The occasional noise from running your gearbox with just your motor and gears is normal. It is due to gear slop, it is normal. You get a bit less of it once you apply thick grease, and it is not a problem once you actually have a load to pull.

2. Confirm that the tappet is actually pressing on sector gear. Assemble the gearbox with the gear set, tappet plate, cylinder head, and nozzle. If the nozzle moves back and forth relatively freely, the tappet is not getting caught on the sector gear.

3. If it actually is getting caught on the sector gear, you can either file the side of the tappet that goes into the channel, or your shimming is incorrect. I'd lean toward the latter.

[RainyEyes]

Originally Posted by pestobanana

1. The occasional noise from running your gearbox with just your motor and gears is normal. It is due to gear slop, it is normal. You get a bit less of it once you apply thick grease, and it is not a problem once you actually have a load to pull.

2. Confirm that the tappet is actually pressing on sector gear. Assemble the gearbox with the gear set, tappet plate, cylinder head, and nozzle. If the nozzle moves back and forth relatively freely, the tappet is not getting caught on the sector gear.

3. If it actually is getting caught on the sector gear, you can either file the side of the tappet that goes into the channel, or your shimming is incorrect. I'd lean toward the latter.

Thanks for the reply!

So I think I've shimmed it properly... but there's always noise when the tappet plate is installed regardless of if there is a load.

The sector gear is still free spinning when the tappet plate is installed, so I'm going to rule out tappet plate pressing down on it being the cause.

The only other thing is that the tappet plate is rubbing up against the gearbox. I tried filing it down by maybe a millimeter but it doesn't seem to alleviate anything. Is friction between the tappet plate and the gearbox normal? It is still free-moving.

I think it's note worthy that there's a chunk of the tappet plate that's missing. There's a 1 mm semicircle on the side that is on the left side, that is, the side that does not engage the sector gear (the side opposite to the flag looking thingy). I think it got cut up from something but I have no idea when/where...

There's just that high pitch whine whenever everything is installed and sounds awful :/

[lurkingknight]

I feel that chirps and whines can be from things being slightly of axis or malformed. I've also had shims make chirps and whines as well as they free spin on the axles sometimes depending on the orientation of the gun. I've built a gun with shs 13:1s that chirps very loudly and distinctively but is properly shimmed. After about 20k rounds there's no abnormal wear anywhere and I can't find the source of the noise but the gun runs very efficiently, just with a chirp.

As long as there's no grind and things are not binding, it should be fine.


Keep in mind it could be the sector gear rubbing on the tappet as well somewhere in the rotation of the sector gear.

The deformity in the tappet could be from either the plate flexing in the channels and the tappet pin on the sector hitting only the side of it or it could sometimes be caused by the spacer bushing on the gear axle or the shims themselves. Some tappets are a bit more resistant to deforming like that while ones made of softer materials are fine. Just keep an eye on it. If the fin gets deformed too much it may interfere with proper feeding.

[ThunderCactus]

Are you sure that's not a relief cut so it doesn't hit the axle of the spur gear? Cuts or breaks in plastic will never be clean, there will be material pressed up on the edges, or it will make rough cuts, but never perfectly clean semi-circles.
When the mechbox is totally assembled, does the tappet plate move back and forth freely?
If yes, does it feed?
If yes, it's fine.
If your sector gear is sitting flat on the bearing on the left mechbox shell, it's likely rubbing on something on the shell. You need to have (usually) a 0.3 to 0.5mm shim to pick it up a bit. There's normally quite a bit of room between the sector and tappet plate. It's also possible that in trying to back the sector away from the tappet plate, it might actually be rubbing on the spur gear.
Maybe just take a video and show us.

[RainyEyes]

Originally Posted by ThunderCactus

Are you sure that's not a relief cut so it doesn't hit the axle of the spur gear? Cuts or breaks in plastic will never be clean, there will be material pressed up on the edges, or it will make rough cuts, but never perfectly clean semi-circles.
When the mechbox is totally assembled, does the tappet plate move back and forth freely?
between the sector and tappet plate. It's also possible that in trying to back the sector away from the tappet plate, it might actually be rubbing on the spur gear.
Maybe just take a video and show us.

I don't believe that the tappet plate retracts far enough to touch the spur gear. After further investigation, it doesn't appear that the tappet plate is pressing down on the sector gear, but I still don't know if this whine is normal.



Thank you everyone in advance for trying to diagnose my problem, as well as anyone who had to put up with my mediocre video explaining the problem.

Note: everything in the gearbox is stock.

Vid: https://youtu.be/6zkIqdSzG8Q

1st clip: gear cycle w/ tappet plate installed w/ spring (no cut off lever, cylinder, etc)

2nd clip: gear cycle w/ no load (tappet plate uninstalled)

3rd clip: motor by itself (baseline for noise, thought it might be helpful)

4th clip: examination of gearbox and tappet plate

Thoughts, comments, etc? Is this sound normal or am i just being unreasonable?
Here is a picture of the tappet plate where the "cut" is:



The tappet plate has been filed down as pestobanana's recommendation so the "cut" doesn't look as jagged as it should be.

Edit: apparently the "cut" is normal and I didn't know it was JG's proprietary design? Anyone else know about this?

[lurkingknight]

repeat test 1 but flip the gearbox on the other side, does it make the same noise?

[pestobanana]

What you're hearing is normal. You are perceiving a "noise" when in actuality it is a slight change in gear speed and thus a change in pitch.

Just put your gun back together.

[RainyEyes]

Originally Posted by pestobanana

Just put your gun back together.

https://youtu.be/6LQCti0QyOY

Thanks everyone for your help. The above video is the end result with my meh shimming.

I tried......

[lurkingknight]

the last shot sounds right, little bit of whine but sometimes you won't be able to get rid of it all depending on the gears or shims or bushings. just the way it is.... yay china.

[RainyEyes]

Originally Posted by lurkingknight

the last shot sounds right, little bit of whine but sometimes you won't be able to get rid of it all depending on the gears or shims or bushings. just the way it is.... yay china.

Last shot was when the piston was held back to probably the last tooth after being on full-auto, and then switching to semi which is why that sounded so crisp.

The bushings were press fitted but because they weren't flush w/ the gb i had to press them out... then I realized that they were too tight to go back in so I filed it down and now they're too loose. I think these are 7mm bushings, not 6, like most of them are advertised; so now i have a pack of bushings that are too small.

I'm probably just bad at shimming, no other way around it but I'm guessing them being stock gears don't help. I can't seem to get them to spin freely on their own with no load even though the gears aren't grinding on each other and not enough shims to cause seizing...

In some videos I see gears doing 3-5 rotations with all 3 in an empty gearbox. Mine will only do 1 full rotation when spun by the sector gear.

[lurkingknight]

you're not necessarily looking for number of rotations, you're looking for smoothness of the cycle. I've had some gears turn smoothly for 1 rotation and be perfect and gears that turn for several and be noisy as fuck with proper play in the axles.

Sometimes there's a bur or a shim just wobbling or spinning on an axle that will make noise or a bent axle that causes a bit of wobble, sometimes it's just meshing noise because the gears are shit.